Residential homes and businesses have recently started to re-embrace solar fluid heating technology as a cost efficient way of providing space heat and hot water within a building. Most solar heating systems have a closed looped structure that relies on a pump to drive fluid through a solar collector that absorbs heat from the sun. The solar collector transfers the absorbed heat to the fluid traveling within the collector. The heated fluid is transported to an external heat exchanger that operates to transfer heat from the fluid to another liquid, often water, flowing within the heat exchanger, thereby providing hot liquid to heat the interior spaces of the building or for personal or process use within the building.
While conventional systems use solar collectors to heat fluid in the presence of sunlight, interestingly, they are prone to overheating because they lack the ability to thermally cool fluid when the fluid reaches the maximum operating temperature of the system. In other words, too much solar energy collection may actually damage the system. This situation occurs in a number of common scenarios such as pump failure, lack of heat use in the residence/business, or power failure. During these situations, the fluid within the collector system continues to absorb heat and may surpass the maximum operating temperature of the system, causing the fluid to boil. Overheating typically leads to substantial cost in repairing or replacing the system. Even if the system continues to operate after overheating, the effect of overheated fluid can causes degradation of system performance. For example, boiling fluid leaves a residue in the solar collector that clogs the fluid pathways in the system, thereby inhibiting performance. Also, boiling fluid causes increased pressure and vibration that lead to leaks or breaks in the system piping. As such, the inability of solar fluid heating systems to cool overheated fluid negatively affects the durability of the system, often substantially cutting its service life.
Some solar fluid heating systems include an active cooling mechanism that allows overheated fluid to be cooled. However, these cooling mechanisms are active, meaning the system must positively actuate a means for cooling, such as driving cooler fluid into the overheated fluid, activating an electro-optic material so the solar collector reflects light instead of absorbing it, or electrically activating a three-way valve to divert flow to a cooling mechanism. Active cooling mechanisms are often bulky and more expensive owing to the extra equipment needed to actively cool. Moreover, these active cooling mechanisms require electricity to function and therefore are non-functional at the time of a power failure, precisely when there might be a need for preventing the collector system from overheating.
Attempts have been made to incorporate passive cooling mechanisms, but these systems rely on precise and complicated setup procedures in order to operate properly, and require precise levels of fluid to be present at different operating times in order for the cooling mechanism to operate properly. For example, fluid will flow into the cooling mechanism only if the fluid volume reaches a preset level, ideally corresponding to fluid being at a maximum desired temperature. However, if the system contains less than the ideal volume of fluid, the heated fluid may not reach the required fluid volume when the fluid temperature reaches a maximum operating temperature, i.e. no overheated fluid will flow into the cooling mechanism. Ensuring the proper level of fluid volume is present in the system requires setup by a professional and routine maintenance that are both costly to the average consumer. Therefore, there is a need for a solar fluid heating system incorporating passive cooling that allows for easy setup and maintenance so that the average consumer can setup and operate the system.